Electrical stimulation may be delivered to a patient to treat a variety of symptoms or disorders, such as chronic or episodic pain, gastrointestinal disorders, or pelvic floor disorders. Transcutaneous electrical nerve stimulation (TENS), percutaneous electrical nerve stimulation (PENS), peripheral nerve stimulation (PNS), spinal cord stimulation (SCS), deep brain stimulation (DBS) and cortical stimulation (CS) are examples of electrical stimulation therapies that have proved effective in treating, for example, pain, movement disorders, epilepsy, or other neurological disorders. Stimulation of the gastrointestinal tract can be effective in alleviating gastroparesis and obesity. Stimulation of the sacral nerves, pudendal nerves, or other nerves or tissues associated with the pelvic floor can be effective in alleviating urinary incontinence, fecal incontinence, pelvic pain, and sexual dysfunction.
Many electrical stimulation therapies are delivered by an implantable medical device, e.g., an implantable pulse generator, which is chronically implanted within the patient. One or more implantable leads extending from the implantable medical device carry electrodes for delivery of stimulation energy to a target nerve. For example, leads may be implanted proximate to the spinal cord, pelvic nerves, stomach, gastrointestinal tract, or within the cranium of a patient, e.g., for DBS or CS. The number and positions of the leads and electrodes within the patient is largely dependent on type of stimulation therapy and symptom or disorder treated. Leads and electrodes that deliver SCS, DBS, CS, gastrointestinal stimulation, and pelvic floor stimulation are generally surgically implanted, e.g., via laminectomy, or inserted percutaneously.
A lead typically carries one or more electrodes, e.g., ring electrodes, pad electrodes, or cuff electrodes, disposed at or near the distal end of the lead. Ring electrodes typically extend about the circumference of a lead, and are positioned at respective axial positions along a length of the distal end of the lead. “Paddle leads” typically include a substantially flat insulating body at their distal end, which may have a rectangular solid or otherwise “paddle-like” three-dimensional shape. One surface of the body or “paddle” at the distal end of the paddle lead carries a one or two-dimensional array of pad electrodes. Pad electrodes are substantially flat, three-dimensional conductors, e.g., having a substantially circular cross-section, which may be formed on or attached to the single surface of the paddle. Cuff electrodes are generally embedded within a self-curling or manipulable cuff designed to fit accurately around a specific target peripheral nerve, and are exposed only on the interior surface of the cuff.
In general, the stimulation therapies identified above are delivered to one or more specific target nerves or nerve structures, and may be delivered via leads and electrodes configured to direct stimulation to those particular nerves or nerve structures, and avoid stimulation of other tissues. For example, SCS involves stimulation the spinal cord from within the epidural space at specific targeted locations, such as near vertebral levels T8-T10 to treat axial back pain, over the dorsal columns at vertebral levels T10-L1 to treat pain in the back, legs, ankles or feet, or over the dorsal roots, i.e., proximal to dorsal root entry zone, of L3-S1. Delivering stimulation to the appropriate location on the spinal cord causes paresthesia in the area of perceived pan and may be most effective for neuropathic pain, such as neuropathy or radiculopathy that involves a significant portion of one limb and more than one dermatome.
As another example, PNS involves delivery of stimulation to a specific peripheral nerve via one or more electrodes implanted proximate to or in contact with a peripheral nerve, e.g., cuff electrodes surrounding the peripheral nerve or electrodes on one surface of a flat paddle lead placed in very close proximity to or contact with the nerve. Placing electrodes in very close proximity to the nerve may ensure that only fibers within that nerve are activated at low amplitudes.
For treatment of pain with PNS, the electrodes are implanted in close proximity to the nerve “upstream” from the source of damage or pain, e.g., closer to the spinal cord than the region of damage or pain. When electrodes are implanted upstream, the paresthesia resulting from PNS may extend to a broader area innervated by the target peripheral nerve. The most common upper extremity nerves treated with PNS are the ulnar nerve, median nerve, radial nerve, tibial nerve and common peroneal nerve.